The separation and identification possibilities of some metal–diethyldithiocarbamate (DEDTC) complexes are
investigated by thin-layer chromatography–IR sequential system. DEDTC complexes of metal cations are prepared in a
predetermined optimum pH or pH range. Optimum separation conditions of these complexes and the reproducibilities of their retention factor (Rf) values are investigated on a series of precoated or laboratory-made TLC plates. Rfvalues are determined using the one-dimensional ascending technique. The precision of the procedures is determined for five replicates in terms of standard deviation. Detection limits are also determined for each of the metal complexes. The IR spectra are scanned and interpreted for their precise identifications after preconcentration with a wick-stick procedure for the complexes, giving the overlapped Rfvalues. The complexes could be identified by the aid of IR absorption bands. It has been determined that these IR absorption bands can also be used as reference spectral bands in possible quantitative studies. It is concluded that an efficient and successful qualitative analysis is possible for incompletely-separated complex compounds using an IR spectrophotometer as the TLC detector.
Introduction
In recent years an increasing amount of research has been devoted to the application of metal–ion complexes with carba-mates in chemical and biochemical analysis. This study has been primarily focused on N,N-disubstituted carbamate
chelates because they form stable complexes with many metals. Determinations of carbamates and related compounds (espe-cially pesticides and herbicides) in environmental samples such as drinking water and sewage (1–3), biological materials (4), food (5,6), pharmaceutical agents (7), and steel (8) are also performed frequently.
The choice of metal ions was not accidental. Those studied include both heavy toxic metals (e.g., Cd, Hg, and Pb) and
microelements essential for living organisms (e.g., Co, pre-sent in vitamin B12 and Fe, Cu, Zn, and Mn, components of many enzymes and metalloporphyrins). Sodium diethyldithio-carbamate (Na–DEDTC) is one reagent commonly used for chemical analysis of carbamates. This reagent reacts with many metals creating intrinsic chelates that are insoluble in water. Metal ions bind with DEDTC molecules through two atoms of sulfur, thus forming compounds with tetrasegmental rings. After extraction into an organic phase, metal–ion complexes with DEDTC can be separated by means of different chro-matographic techniques.
TLC separations of metal chelates with DEDTC are most frequently performed on silica gel (9,10) or silica gel G (11,12). Depending on the stationary phase chosen, one- or two-com-ponent mobile phases have been used. Thus, for separation of metal–ion complexes with DEDTC on silica gel, benzene (9,10), xylene (8), toluene (9), 1,2-dichloroethane (9,10), and dichloromethane (9,10) have been used as mobile phases. On silica gel G, metal chelates have been separated by use of mix-tures of benzene with dioxane or toluene (11), diethyl ether, or hexane (12). Additionally, on silica gel-60GF254 metal–DEDTC complexes of Cu2+, Co2+and Ni2+cations have been
success-fully separated with the use of a toluene–cyclohexane mixture (3:1, v/v) as mobile phase (13).
The direct coupling of TLC [high-performance TLC (HPTLC), in fact] and Fourier transform IR (FTIR) was intro-duced in 1989. The in situ measurement of chromatograms and FTIR spectra was extensively studied by Kovar et al. (14). Afterwards, Stahlmann presented a detailed report on HPTLC–FTIR online coupling in 1999 (15). The in situ TLC–diffuse reflectance Fourier transform spectroscopy (DRIFT) system, which requires complete removal of solvent and subtraction of the IR spectrum of the layer measured on the same plate as the sample spectrum, allows both the quali-titave and quantitative characterization of a TLC spot. Because in situ spectra may differ from those obtained in solution or from a KBr pellet, in situ standard and sample spectra must be compared to obtain zone identification. This approach is par-ticularly useful when a TLC–DRIFT-interfaced system is used for monitoring unstable compounds such as
diazonaptha-R. Gürkan1,* and S. Savascı2
1University of Cumhuriyet, Science and Arts of Faculty, Department of Chemistry, 58140 Sivas and 2BAÜ Science and Arts of Faculty,
Department of Chemistry, 10100 Balikesir, Turkey
Journal of Chromatographic Science, Vol. 43, July 2005
Investigation of Separation and Identification
Possibilities of Some Metal–DEDTC Complexes
by Sequential TLC–IR System
* Author to whom correspondence should be addressed: email rgurkan@cumhuriyet.edu.tr.
Abstract
Journal of Chromatographic Science, Vol. 43, July 2005
quinones (16). In situ spot analysis requires blank experiments and correction except for situations having strong IR back-ground absorption. The final IR spectra of a TLC spot are also obtained by overlapping sample and background measure-ments. Many approaches to FTIR measurement of IR spectra of TLC spots are made to reduce the problems involved in possible background interference on TLC plates (17–19).
This study focuses on the scan and interpretation of the IR spectra after preconcentration of incompletely-separated spots at the end of the wick stick. Chromatographic behavior and identification possibilities of metal–DEDTC chelates were investigated using the IR characteristic absorption bands.
Experimental
Apparatus
A TLC applicator (Bibby Sterilin Ltd., Staffordshire, U.K.), UV lamp with two wavelengths (operating at 254 and 366 nm) for detection and pH meter having a measurement sensitivity of ± 0.02 (3010 Mark, Jenway Co., Essex, U.K.) were used. Addi-tionally, a Unicam Mattson 1000 IR spectrometer (Unicam Ltd., Cambridge, U.K.) was used in the wavelength range of 400–4000 cm–1with a resolution of 2 cm–1for scanning and
collecting the IR spectra of metal–DEDTC complexes. Reagents
Four different adsorbents (Silica gel-60H, -60HF254,
-60GF254, and -60PF254) were used for the purpose of using one
adsorbent type that is differentiated with or without the fluo-rescent indicator (F254), (Merck, Darmstadt, Germany), acetic
acid–sodium acetate buffer solution (pH 4–6), and Na-DEDTC for chelation of metal cations were used. All other reagents were also of analytical grade.
Test solutions
The stock test solutions (1%, w/v) were chloride or nitrate salts of Cu, Ni, Co, Cr, Mn, Zn, Pb, Cd, Hg, Bi, As, and Sb (Merck). Working solutions were prepared by diluting the stock solution with water. Doubly-distilled water was used to prepare and dilute the test solutions throughout the experimental studies. Solutions of 0.1% and 1.0% (w/v) chelating reagent in water were used on the TLC plates and preconcentration pro-cedure, respectively.
Detection
The following detection systems were used to locate the analytes on chromatoplates: (i) dithizone (0.02%, w/v) in
ace-tone for Zn2+, Cd2+, Pb2+, and Hg2+ions; and (ii) natural colors
of their complexes for As3+, Sb3+, Bi3+, Mn2+, Co2+, Ni2+, Cu2+,
and Cr3+ions.
Mobile phase
Benzene, dichloromethane, dichloromethane–xylene (1:1, 1:4, and 4:1, v/v), dichloromethane–petroluem ether (1:1, 1:4, and 4:1, v/v), acetone–benzene (1:1, 1:4, and 4:1, v/v), ben-zene–isobutylmethylketone (1:1, 1:4, and 4:1, v/v) and ethyl-acetate–toluene (1:1, 1:4, and 4:1, v/v) mixtures were used.
Stationary phase
Laboratory-made TLC plates, which were coated with four different adsorbent (silica gel 60H, 60HF254, 60GF254, and 60PF254), and commercial TLC plates, which were precoated with Silica gel-60F254, were used for experimental studies. Preparation of TLC plates
TLC plates were prepared by suspending silica gel with water in a 1:2.5 (w/v) ratio. The resulting slurry was mechan-ically shaken for several minutes, following the recommen-dations of a manufacturer. Afterward, the slurry was coated onto glass plates using a TLC applicator to give layers of 0.50- and 0.75-mm thicknesses for analytical and preparative purposes, respectively. The plates were air-dried at room tem-perature and then activated by heating at 100°C for 1 h. After activation, the plates were stored in an air-tight chamber until use.
The chelating procedure
The stock cation solutions were adjusted to a pH range of 4–6 with a CH3COOH–CH3COONa buffer solution. The solu-tions were mixed with an excess of ligand for the preparation of metal–DEDTC complex solutions and then extracted into the chloroform phase. The extraction procedure provided some advantages such as preconcentration and selectivity. Addition-ally, to prevent the clustering of complexes, the organic phase has also eliminated some of the drawbacks such as chromato-graphic tailing and dispersion of Rfvalues. The organic phase was separated from the aqueous phase and prepared for injec-tion by drying with anhydrous Na2SO4solid. Chloroform was selected as the organic phase because it provided additional stability to all of the metal complexes (19).
Chromatographic procedures
Approximately 10 µL of the complex solutions was spotted separately on the TLC plates by using adjustable Fisher pip-ettes. The spots were air-dried and the chromatograms were developed, allowing the solvent to ascend up to 10 cm from the point of application in all cases. After development, the chro-matograms were air-dried at room temperature and the com-plex spots were visualized by either their natural colors on the plate or exposure to ammonia vapor after spraying the TLC plate with 0.02%(w/v) solution of dithizone in acetone for colorless complexes. When dithizone solution is sprayed onto the TLC plate, Cd2+- and Hg2+-containing zones turn yellowish
orange in color, whereas Pb2+- and Zn2+-containing zones turn
to a reddish/pink color. The Rf values for the detected spots were established. Afterward, the standard deviation and relative standard deviation of the Rf values were calculated.
To study the effect of concentration on the separation or Rf values of metal complexes, 10 µL of the complex solutions prepared at the various concentrations (in a concentration range of 100–1000 mg/L) were spotted on the chromatograms. The plates were developed in dichloromethane and benzene separately, dried, and the spots were then detected as men-tioned previously.
The limits of detection (LOD) of the metal complexes were determined by spotting 1–10 µL of the complex solutions of
Journal of Chromatographic Science, Vol. 43, July 2005
decreasing concentrations on the TLC plates, which were developed with benzene. The spots were visualized using the appropriate detector. This was repeated until no detection was possible. The procedure was repeated three times for each metal complex. The amount of salt only detectable in solution was taken as the LOD.
Wick-stick procedure
Each of the complexes containing the spots were sepa-rated and concentsepa-rated from the coating matrix using the wick-stick procedure. The wick-stick procedure is described as follows:
Wick sticks are triangular wedges of compressed KBr powder that are porous. They are approximately 8 mm wide at the base, 25 mm in height, and 1.25 mm thick. The spot, which is sepa-rated by scraping from plate, is placed in a vial that is approxi-mately 5 cm in height and 1.25 cm in diameter. Chloroform, which easily dissolves the relevant complex, is then added to a volume of 1/
8–3/8of the vial. The wick stick is inserted in a
metal holder and dropped into the vial. A cap with a hole in it is placed on top. The complex solution rises to the tip of the KBr wedge and evaporates from the tip. Soluble complex material rises to the tip along with the solvent and is concentrated there as the solvent evaporate. Insoluble
mate-rial is left behind. The tip is broken off and a micro-KBr disk is prepared for the IR analysis. The effect of strong IR-absorbing matrices as silica gel on the IR spectra of spots is completely removed by solvent extraction with CHCl3. Also, the
complex contents of the spots are free of adsorbents that hinder the IR spectrum (19–21).
Results and Discussion
Plates prepared from silica gel were of almost the same quality as that of the ready-made plates prepared in a stan-dardized manner by recognized manu-facturing firms, providing well-formed and compact spots for the chromato-graphed metal complexes. Developments were made using solvents and solvent mixtures having medium polarity (such as dichloromethane, benzene, toluene, xylene, and petroleum ether) and high polarity (such as methanol, acetone, ethyl acetate, and methyl-isobutyl-methylketone). The development time for a 10-cm run was approximately 15 min. It was found that the most effective eluent systems were solvent and solvent mixtures, which have medium polarity in chromatographic separations. The identification in authentic TLC is based
on the Rfvalue. After spot identification obtained with visual
observation, the Rfvalues were established as the ratio of the
distance of each spot to the front of the solvent or solvent system. The reported Rfvalues are the averages of five repeated
observations for precision. The results of this study are sum-marized in Table I.
It was suggested that dichloromethane–petroleum ether mixture (9:1, v/v) be used as the most effective eluent system for the separations of metal–DEDTC complexes (20). In this study, benzene and dichloromethane were found as the most effective eluent systems, separately. However, the reproducibili-ties of the Rfvalues were poor because of tailing or
band-broadening caused by high application loading into the plate for some complex species such as MnL2, CrL3, AsL3, and CdL2
with both of the solvents.
The effect of the concentration on the Rfvalues was
exam-ined in a concentration range of 100–1000 mg/L. It was observed that the Rf values of the Fe(III), Sn(II), Sn(IV), and
Ag(I) complexes decreased at a considerable ratio in low con-centrations; namely; this was dependent upon the concentra-tion. Additionally, these metal complexes, except for Fe(III), gave approximately the same Rf values with both
dichloro-methane and benzene in Tables II and III. However, the other Table I. Rf, Standard Deviation in RfValues, and LOD of Metal–DEDTC
Complexes Developed with Dichloromethane and Benzene* on TLC Plate†
Metal Rf SD RSD Confidence interval LOD
complex (ave.) (Rf) (Rf) (95% confidence level) (µg)
AsL3 0.64–0.38* 0.05–0.04* 6.25–10.52* 0.05–0.05* 2.50* SbL3 0.73–0.37 0.07–0.03 9.58–8.11 0.09–0.04 2.60 PbL2 0.75–0.48 0.04–0.03 5.33–6.25 0.05–0.04 0.50 ZnL2 0.84–0.69 0.03–0.03 3.57–3.35 0.04–0.04 0.40 BiL3 0.63–0.35 0.03–0.03 4.76–8.57 0.04–0.04 0.75 CuL2 0.86–0.68 0.03–0.03 3.49–4.41 0.04–0.04 0.25 MnL2 0.62–0.34 0.08–0.02 12.90–5.88 0.1–0.03 0.65 CdL2 0.71–0.49 0.07–0.05 9.86–10.20 0.09–0.09 2.00 HgL2 0.79–0.60 0.07–0.03 8.86–5.00 0.09–0.04 1.75 CrL3 0.58–0.33 0.08–0.02 13.79–6.06 0.1–0.03 3.5 CoL2 0.71–0.51 0.07–0.02 9.86–3.92 0.09–0.03 0.30 NiL2 0.78–0.42 0.07–0.03 8.97–7.14 0.09–0.04 0.28 * L = DEDTC.
†Precoated with commercial silica gel 60F254 adsorbent with 10- × 10-cm, 0.20-mm thickness for five repeated runs. SD = standard deviation and RSD = relative standard deviation.
Table II. Metal–DEDTC Complexes with Behaviors Dependent on Concentration when Developments Made with Dichloromethane and Benzene on TLC Plates
Retention factors (Rf) Concentration
(mg/L) Fe (DEDTC)3 Sn (DEDTC)2 Sn(DEDTC)4 Ag–DEDTC
100 0.56–0.24* 0.54–0.23 0.52–0.25 0.48–0.21
250 0.61–0.28* 0.60–0.27 0.55–0.28 0.51–0.25
500 0.62–0.29* 0.61–0.29 0.56–0.29 0.52–0.26
750 0.62–0.29* 0.62–0.29 0.56–0.29 0.52–0.26
1000 0.63–0.29* 0.63–0.29 0.57–0.29 0.53–0.27
* Developments made with benzene.
Journal of Chromatographic Science, Vol. 43, July 2005
remaining metal complexes expressed an unchanged chro-matographic behavior with decreasing concentration. Because this dependence was more pronounced in terms of a chro-matographic result, the previously-mentioned metal complexes were eliminated for subsequent studies.
An attempt was also made to establish the LOD of the method with the analysis of standard water samples con-taining only one cation or its complex with benzene on TLC plates for the cations in question. The results are shown in Table I. Because the purpose was to identify and detect the metal complexes that have overlapping Rfvalues, no attempt
was made to establish the applicability of the proposed TLC–IR system to the analysis of real samples containing the rele-vant metal cations.
The complexes that have overlapping Rfvalues in
develop-ment with dichloromethane could successfully be distin-guished by interpretation of their characteristic IR bands. The Co(II)– and Pb(II)–DEDTC complexes having the fully-overlapped νC=Nvibration frequencies can also be
differenti-ated by giving different νC=Svibration frequencies (Table IV).
It can be observed that Bi(III)–, As(III)–, and Mn(II)–DEDTC complexes having the overlapped Rf
values are identified by help of both νC=N
and νC=Svibration frequencies. Again, it
was observed that Ni(II)– and Hg(II)– DEDTC complexes having the same Rf
values will be differentiated by fully exhibiting the different vibration fre-quencies of νC=Ndouble-bond because of
the interaction of the C–N bond with active –OH groups of silica gel. It was concluded that these metal complexes, having the same Rfvalues, had at least
one or more (νC=N and νC=S) vibration
frequencies, and they will be be identifi-able from real samples by a TLC–IR sequential system, although no chro-matographic separation has occurred.
Also, the Zn(II)–/Cu(II)–DEDTC, Pb(II)–/ Cd(II)–/Ni(II)–DEDTC, and As(III)–/Sb(III)–/Mn(II)–/Cr(III)–DEDTC complex groups give the overlapping Rf
values with benzene. Nevertheless, these complexes can be differentiated by the help of both the νC=Nand νC=Svibration
frequencies. It can easily be seen that the characteristic νC=Nand νC=S
vibra-tion frequencies for these complexes are partly or fully different from each other (Table V).
Finally, a conclusion was drawn that any metal–DEDTC complex, except the Cr(III) cation in the high concentrations (1000 mg/L; because of gel formation in the organic phase during extraction and a low extractability), will be useful in the identification of metal cations present in real samples.
Conclusion
Identification of an unknown compound in a complex matrix is always difficult. With each passing year and complicated
Table III. RfValues of Concentration-Depended Complexes Developed with Dichloromethane and Benzene on TLC Plates*
Retention factors (Rf) Complexes Dichloromethane Benzene
Na–DEDTC 0.84 ± 0.028† 0.66 ± 0.022†
Fe (DEDTC)3 0.64 ± 0.033 0.31 ± 0.012
Sn (DEDTC)2 0.63 ± 0.031 0.30 ± 0.016
Sn (DEDTC)4 0.63 ± 0.028 0.30 ± 0.015
Ag–DEDTC 0.61 ± 0.024 0.27 ± 0.017
* Initially coated with silica gel HF254 adsorbent with 20- × 20-cm dimension at 0.50-mm thickness for six repeated runs.
†The average R
fand its standard deviation for six replicate measurements.
Table IV. Separation and Identification of Metal–DEDTC Complexes with Overlapping RfValues in Size of SD by Characteristic IR-Absorbing Bands* after Preconcentration with Wick-Stick Procedure
Vibration frequency (cm–1)
Complex Rf Rf± SD ννC=Nstretching ννC=Sstretching
CoL2 0.71 0.71 ± 0.07 1489, 1455, 1274 1217, 1149, 1138, 1081 CdL2 0.71 0.71 ± 0.07 1501, 1455, 1274 1206, 1149, 1092, 1081 SbL3 0.73 0.73 ± 0.07 1501, 1467, 1274 1194, 1149, 1092, 1080 PbL2 0.75 0.75 ± 0.04 1489, 1455, 1274 1206, 1138, 1092, 1069 BiL3 0.63 0.63 ± 0.03 1501, 1467, 1274 1240, 1194, 1115, 1092 AsL3 0.64 0.64 ± 0.04 1501, 1455, 1274 1194, 1149, 1115, 1092, 1001 MnL2 0.62 0.62 ± 0.08 1489, 1455, 1262 1206, 1149, 1092, 1035 HgL2 0.79 0.79 ± 0.07 1489, 1455, 1262 1206, 1138, 1092, 1069 NiL2 0.78 0.78 ± 0.07 1523, 1444, 1274 1206, 1149, 1092, 1069
* In development with dichloromethane on plates.
Table V. Separation and Identification of Metal–DEDTC Complexes with Overlapping RfValues in Size of SD by Their Characteristic IR-Absorbing Bands* after Preconcentration with Wick-Stick Procedure
Vibration frequency (cm–1)
Complex Rf Rf± SD ννC=Nstretching ννC=Sstretching
AsL3 0.38 0.38 ± 0.04 1501, 1455, 1274 1194, 1149, 1115, 1092, 1069, 1001 SbL3 0.37 0.37 ± 0.03 1501, 1467, 1274 1194, 1149, 1115, 1092 BiL3 0.35 0.35 ± 0.03 1501, 1467, 1274 1240, 1194, 1115, 1092 MnL2 0.34 0.34 ± 0.02 1489, 1455, 1262 1206, 1149, 1092, 1035 CrL3 0.33 0.33 ± 0.02 1501, 1455, 1274 1194, 1126, 1103, 1001 PbL2 0.48 0.48 ± 0.03 1489, 1455, 1262 1194, 1149, 1092, 1069 CdL2 0.49 0.49 ± 0.05 1501, 1455, 1274 1206, 1149, 1092, 1035 NiL2 0.51 0.51 ± 0.03 1523, 1444, 1274 1266, 1149, 1092, 1069 ZnL2 0.69 0.69 ± 0.03 1501, 1433, 1274 1206, 1149, 1092, 1069 CuLv 0.68 0.68 ± 0.03 1512, 1467, 1274 1206, 1149, 1092, 1081
* In development with benzene on plates.
Journal of Chromatographic Science, Vol. 43, July 2005
sample requiring analysis, demands for accuracy and speed of analysis have also increased. In order to overcome these prob-lems, chemical methods have been replaced by more complex hyphenated instrumental approaches. A sequential technique that has great analytical potential is the chromatographic FTIR system. One of the important aspects of improving these systems is the investigation of “analytical windows” in IR spectra according to components separated. The analytical window can be defined as the spectral interval that is useful to the analytical evaluation of a species regardless of the com-plexity of the matrix containing the analyte. In samples with complex matrices, a theoretical suggestion of these analytical windows is not a very applicable technique. On the other hand, when analytical species with the same behaviors are in ques-tion, the availability of such suitable windows is also rare. The fact that chromatography and IR spectrophotometer are com-plementary has also been demonstrated here. The qualitative vibration bands (those of C–N and C=S bonds) concerning metal complexes is sufficient for more quantitative study of their degree shifts because of different central cations. After the analytical species having different Rfvalues are separated by
TLC, these peaks will be a good measure for quantitative deter-mination of each cation. In this case, such analysis will be performed with success in the TLC–IR sequential system, and suitable data to quantitate these complexes from a mixture containing metal complexes is directly acquired by FTIR.
In this study, instead of identifying the pairs of cations by the FTIR method directly from a solution without chromatog-raphy, the TLC–IR sequential system was preferred as an instrumental remedy to a poor TLC separation for the relevant complex pairs. In this context, the TLC–IR sequential system can be seen as an alternative, selective, and semiquantitative analysis method for small-budget laboratories.
Acknowledgments
The authors are especially grateful to the Cumhuriyet Uni-versity of Research Fund Accountant Office officials for their generous assistance in supplying the chemicals. Financial sup-port for this work was provided by Cumhuriyet University, Research Fund Accountant Office under MSc thesis project with F-32 code. The authors thank Prof. Dr. Mehmet Akçay and all of their colleagues for assistance and providing the labora-tory facilities for this work.
References
1. S. Ichinoki. Studies of the simultaneous determination of trace metals by high performance liquid chromatography. Bunseki
Kagaku43(2): 185–86 (1994).
2. A.R. Timerbaev, O.M. Petrukhin, and Y.A Zolotov. Evaluation of the possibility of high performance column chromatography for the separation and determination of metals as chelates. Zh. Anal.
Khim.41(12): 1509–17 (1986).
3. R.M. Smith, A.M. Butt, and A. Thakur. Determination of lead,
mercury and cadmium by liquid chromatography using on
column derivatisation with dithiocarbamates. Analyst110(1):
35–37 (1985).
4. G. Drasch. Optimization of the trace detection of heavy metals of toxilogical interest by reversed-phase high pressure liquid chro-matography of their thiocarbamates. Fresenius’ J. Anal. Chem.
325(3): 285–89 (1986).
5. K. Friedrichs, H.D. Winkeler, and P. Gerhards. Determination of dithiocarbamate residues in foodstuff by headspace gas-chro-matography and flame photometric detection. Z. Lebensm.
Unters. Forsch.201(1): 69–73 (1995).
6. N. Kibune, N. Higashisaka, M. Nakamura, and Y. Maekawa. Rapid analysis method of dithiocarbamate pesticides in agricul-tural products by high performance liquid chromatography.
J. Food Hygenic Soc. Japan 36(2): 244–51 (1995).
7. M.B. Evans and M.S. Smith. A comparative study of the chro-matography of hydroxilated dialkyl dithiocarbamates as models
for drug metabolites. Chromatographia39(9-10): 569–76 (1994).
8. A. Asolkar, A.A. Kumar, P. Pandey, and R. Bhardwaj. TLC resolu-tion studies of some metal-piperidinedithiocarbamate complexes on various surfactant impregnated silica gel-GP plates. J. Liq.
Chromatogr.15(10): 1689–1701 (1992).
9. G. Soundararajan and M. Subbaiyan. Thin layer chromatographic behavior and separation of Thallium-I and Thallium-III valencies as their neutral N,N-disubstituted dithiocarbamates. Sep. Sci.
Technol.18(7): 645–55 (1983).
10. A.R. Timerbaev, O.M. Petrukhin, and Y.A. Zolotov. Liquid adsorp-tion chromatography of chelates-mechanism of the separaadsorp-tion of diethyldithiocarbamates by thin layer chromatography. J. Anal.
Chem. USSR37(8): 1039–47 (1982).
11. R.K. Shukla and A. Kumar. Spectrophotometric determination of molybdenum after separation of its pyrolidinedithiocarbamate
by adsorption of naphthalene. J. Anal. Chem. USSR 46(11):
1609–11 (1991).
12. B. Martinez, J.C. Orte, M. Miro, G. Crovetto, and J. Thomas. Thin layer chromatography of N,N-disubstituted
dithiocarba-mates of nickel (II) and cobalt (II). J. Chromatogr. A655(1): 45–49
(1993).
13. S. Ergül. Qualitative analysis of Cu2+, Co2+, and Ni2+cations using
thin-layer chromatography. J. Chromatogr. Sci.42: 121–24 (2004).
14. K.A. Kovar, H.K. Ensslin, O.R. Frey, S. Reinas, and S.C. Wolff. Identification and estimation of complex mixtures by direct
TLC-IR online coupling. GIT Special Chromatographia 11:
95–98,100–101 (1991).
15. S.A. Stahlmann. Ten year report on HPTLC-FTIR online coupling.
J. Planar Chromatogr.-Mod. TLC12(1): 5–12 (1999).
16. P.R. Griffiths. Chemical Infrared Fourier Transform Spectroscopy,
Chemical Analysis, vol. 43. Wiley-Interscience, New York, NY,
1975, p. 256.
17. M.P. Fuller and P.R. Griffiths. Infrared microsampling by diffuse
reflectance fourier transform spectrometry. Appl. Spectrosc. 34(5):
533–39 (1980).
18. K.H. Shafer and P.R. Griffiths. Sample transfer accessory for thin layer chromatography/Fourier transform infrared spectrometry.
Anal. Chem.58(13): 2708–14 (1986).
19. S¸ . Savas¸cı and M. Akçay. The determination of some heavy metal
cations by TLC/Photodensitometry. Turk. J. Chem.20(2): 146–52
(1996).
20. I. Hubertus, G.J. De Jong, U.A.Th. Brinkman, and R.W. Frei. Trace enrichment and separation of metal ions as dithiocarbamate
complexes by liquid chromatography. Anal. Chem. 59(1): 98–101
(1987).
21. D.W. Mayo, F.A. Miller, and R.W. Hannah. “Course notes on the interpretation of Infrared and Raman spectra”. In Infrared Spectra
of Mixtures. John Wiley & Sons, New York, NY, 2004, pp.
461–504.
Manuscript received October 14, 2004; revision received April 25, 2005.
